1. Field
The present invention relates to the electronics manufacturing industry and more particularly to the process of etching features in a multi-layered masking stack.
2. Discussion of Related Art
As the feature size of the device pattern gets smaller than 100 nm, the critical dimension (CD) requirement of features becomes a more important criterion for stable and repeatable device performance. Photoresist films must get thinner for better resolution at a given optical transparency, so sufficient etch resistance becomes more difficult to attain without a hard mask. Striations in the sidewalls of features are one of main sources of CD variation. Generally, striations are believed to initiate in the sidewalls of the mask and propagate downward into the substrate as it is etched to form a feature. Striations occur as a result of both the photolithographic process and the etch process. Initial line edge roughness (LER) roughness, caused by the diffusion of acids during develop can be exacerbated during etch. Striations are typically quantified with an LER measurement taken from a top down view of the feature. Furthermore, the mechanical softness, rough as-developed sidewalls, and reduced thickness of 193 nm ArF photoresist (PR) combine to make it difficult to etch a sub-100 nm feature without striations.
For a smaller LER value, it is necessary to use either a more etch resistant and/or thicker mask material, or improve the selectivity of the etch process. The former option increases the number of production steps, resulting in higher cost per wafer as well as complex integration issues. However, the latter option typically displays several etch process limitations, such as severe loading effects and even increased LER resulting from irregular polymer deposition which negatively impact CD control.